The present invention relates to a centrifugal blood pump apparatus for pumping a medical fluid, typically blood.
In recent medical treatment, centrifugal blood pumps are increasingly used in artificial heart/lung units for extracorporeal blood circulation. Centrifugal pumps of the magnetic levitation type wherein a driving torque from an external motor is transmitted to an impeller through magnetic coupling are commonly used because the physical communication between the blood chamber of the pump and the exterior can be completely excluded and invasion of bacteria can be prevented.
The present applicant proposed a centrifugal blood pump disclosed in U.S. Pat. No. 5,947,703.
The centrifugal blood pump includes the housing having the inlet port and the outlet port for blood and adapted to receive blood therein, and the impeller adapted to rotate within the housing for feeding blood by a centrifugal force developed during rotation, the uncontrolled magnetic bearing means (impeller rotational torque generation section) for magnetically supporting the impeller, and the controlled magnetic bearing means (impeller position control section) for magnetically supporting the impeller. The controlled magnetic bearing means and the uncontrolled magnetic bearing means cooperate such that the impeller rotates while it is held at a predetermined position within the housing. The impeller has a large number of hydrodynamic pressure grooves formed on its bottom surface (lower surface). Owing to the action of the hydrodynamic pressure groove, the impeller is attracted toward the impeller rotational torque generation section 3, when the impeller position control section is not operative (in other words, when the operation of electromagnet stops). However, at this time, the impeller rotates at a position spaced at a slight distance from the inner surface of the housing without contacting the inner surface thereof owing to the hydrodynamic bearing effect formed between the hydrodynamic pressure groove and the inner surface of the housing.
The above-described centrifugal blood pump apparatus is of a magnetic levitation type and has a favorable effect. The hydrodynamic pressure groove of the centrifugal blood pump apparatus acts when the impeller position control is stopped, i.e., when the operation of the electromagnet attracting the impeller thereto is stopped because of failure of the controlled magnetic bearing means (impeller position control section) for the control of the impeller. That is, the hydrodynamic pressure groove is not utilized in a normal rotation of the impeller. During the rotation of the impeller made only by the action of the hydrodynamic pressure groove, there is a fear that hemolysis occurs when the impeller has a small number of rotations. Since the impeller is levitated by a magnetic force, it is necessary to provide the centrifugal blood pump apparatus with an impeller position sensor. Thus it is very difficult to make the centrifugal blood pump apparatus compact. Further an electric power for the magnetic levitation of the impeller is required.
Therefore it is an object of the present invention to provide a centrifugal blood pump apparatus not of a magnetic levitation type but of a type in which the impeller is rotated without contacting a housing by utilizing the action of a hydrodynamic pressure groove. This construction eliminates the need for the use of a position sensor. Thereby it is possible to make the centrifugal blood pump apparatus compact. Further it is possible to secure a predetermined distance between the housing and the impeller and thereby reduce generation of hemolysis.